So here we go - a complete transcript of Digital Foundry's discussions on the Xbox One architecture with two integral members of the team that helped create the hardware. We're looking at around an hour's worth of very dense tech talk here, much of which you will not have seen before.
But first, a little background. How did this opportunity come about? At Gamescom in August, it became clear that Microsoft was looking to adjust its stance on how it talked about its hardware from a technological perspective. Almost certainly this came about owing to an overall spec sheet that does not look too encouraging compared to the equivalent metrics being offered by Sony for the PlayStation 4, and it was clear that gamer interpretations of some of the specs didn't quite square with Microsoft's thinking over its design.
Over and above the upcoming console war though, it's clear that Xbox One has been designed with a very different philosophy in mind, with some ambitious tech powering elements such as concurrent apps and multiple virtual machines. There's a very different approach to GPU compute too - not to mention the whole balance argument. Coming out of the experience, it was clear that this was a story that the architects were passionate about and very much wanted to tell.
That said, Microsoft does have a history in sharing in-depth data on the make-up of its console architectures, and its presentation at Hot Chips 25 this year at Stanford University indicated that the design team were willing to talk in detail about the silicon to a degree beyond what Sony are willing to share - which is perhaps understandable on the PlayStation front when you have a spec sheet that essentially does most of the talking for you.
So the question many of you are no doubt asking is, are we looking at a free-flowing technical discussion or a PR exercise? Well, let's not kid ourselves - every interview that reaches publication is some form of public relations for the interviewee and that applies equally whether we're talking to Microsoft, Sony or anybody else. Perhaps the lingering disappointment for us with our Mark Cerny interview was the fact that it quickly became evident he was not going to let us into much that he hadn't already covered elsewhere. It's also fair to say that the impressive specs, well-rounded line-up and a phenomenally well-managed PR strategy have left Sony in a very favourable position, with nothing to prove - for now, at least.
For Microsoft, things are clearly very different. It's a case of explaining a design philosophy that core gamers aren't connecting with so easily, while at the same time getting across the message that the technological prowess of a games console isn't limited just to the compute power of the GPU or the memory set-up - though ironically, in combination with the quality of the development environment, these are the very strengths that allowed Xbox 360 to dominate the early years of the current-gen console battle.
Onto the discussion then - perhaps Digital Foundry's most expansive hardware interview yet, kicking off with the requisite conference call introductions.
Xbox One comes from much the same team that designed Xbox 360, shown here in its classic launch format. The design team opted to match a state-of-the-art (for its time) graphics chip with a multi-core approach to the GPU at a time when a single, powerful processor was the vogue in PC design.
Andrew Goossen: My name is Andrew Goossen - I'm a technical fellow at Microsoft. I was one of the architects for the Xbox One. I'm primarily involved with the software side but I've worked a lot with Nick and his team to finalise the silicon. For designing a good, well-balanced console you really need to be considering all the aspects of software and hardware. It's really about combining the two to achieve a good balance in terms of performance. We're actually very pleased to have the opportunity to talk with you about the design. There's a lot of misinformation out there and a lot of people who don't get it. We're actually extremely proud of our design. We think we have very good balance, very good performance, we have a product which can handle things other than just raw ALU. There's also quite a number of other design aspects and requirements that we put in around things like latency, steady frame-rates and that the titles aren't interrupted by the system and other things like that. You'll see this very much as a pervasive ongoing theme in our system design.
Nick Baker: I'm Nick Baker, I manage the hardware architecture team. We've worked on pretty much all instances of the Xbox. My team is really responsible for looking at all the available technologies. We're constantly looking to see where graphics are going - we work a lot with Andrew and the DirectX team in terms of understanding that. We have a good relationship with a lot of other companies in the hardware industry and really the organisation looks to us to formulate the hardware, what technology are going to be appropriate for any given point in time. When we start looking at what's the next console going to look like, we're always on top of the roadmap, understanding where that is and how appropriate to combine with game developers and software technology and get that all together. I manage the team. You may have seen John Sell who presented at Hot Chips, he's one of my organisation. Going back even further I presented at Hot Chips with Jeff Andrews in 2005 on the architecture of the Xbox 360. We've been doing this for a little while - as has Andrew. Andrew said it pretty well: we really wanted to build a high-performance, power-efficient box. We really wanted to make it relevant to the modern living room. Talking about AV, we're the only ones to put in an AV in and out to make it media hardware that's the centre of your entertainment.
Digital Foundry: What were your takeaways from your Xbox 360 post-mortem and how did that shape what you wanted to achieve with the Xbox One architecture?
Nick Baker: It's hard to pick out a few aspects we can talk about here in a small amount of time. I think one of the key points... We took a few gambles last time around and one of them was to go with a multi-processor approach rather than go with a small number of high IPC [instructions per clock] power-hungry CPU cores. We took the approach of going more parallel with cores more optimised for power/performance area. That worked out pretty well... There are a few things we realised like off-loading audio, we had to tackle that, hence the investment in the audio block. We wanted to have a single chip from the start and get everything as close to memory as possible. Both the CPU and GPU - give everything low latency and high bandwidth - that was the key mantra.
Some obvious things we had to deal with - a new configuration of memory, we couldn't really pass pointers from CPU to GPU so we really wanted to address that, heading towards GPGPU, compute shaders. Compression, we invested a lot in that so hence some of the Move Engines, which deal with a lot of the compression there... A lot of focus on GPU capabilities in terms of how that worked. And then really how do you allow the system services to grow over time without impacting title compatibility. The first title of the generation - how do you ensure that that works on the last console ever built while we value-enhance the system-side capabilities.
Digital Foundry: You're running multiple systems in a single box, in a single processor. Was that one of the most significant challenges in designing the silicon?
Nick Baker: There was lot of bitty stuff to do. We had to make sure that the whole system was capable of virtualisation, making sure everything had page tables, the IO had everything associated with them. Virtualised interrupts.... It's a case of making sure the IP we integrated into the chip played well within the system. Andrew?
Andrew Goossen: I'll jump in on that one.....
Full Transcript
http://www.eurogamer.net/articles/digitalfoundry-the-complete-xbox-one-interview
The ability to run apps concurrently with the game with zero impact on performance required a significant amount of engineering, but the final result does work very well. What will make or break the system will be the quality of the apps themselves - certainly functions like party set-up and video editing work nicely.
The news that first-party exclusive Killer Instinct operates at a native resolution of 720p has surprised - and not impressed - a lot of gamers.
Forza Motorsport 5 is Xbox One's standout title, operating at full 1080p with a smooth 60fps update. As an embedded first party studio, Turn 10 would presumably have had more intimate access to the new hardware at an earlier stage than other developers.
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